Hybrid energy storage devices, also known as asymmetric supercapacitors or hybrid battery/supercapacitors, combine battery electrodes and supercapacitor electrodes to produce devices having a unique set of characteristics including cycle life, power density, energy capacity, fast recharge capability, and a wide range of temperature operability. Hybrid lead-carbon energy storage devices employ lead-acid battery positive electrodes and supercapacitor negative electrodes. See, for example, U.S. Pat. Nos. 6,466,429; 6,628,504; 6,706,079; 7,006,346; and 7,110,242.
The positive electrode of a hybrid energy storage device effectively defines the active life of the device. Just as with lead-acid batteries, the lead-based positive electrode typically fails before the negative electrode. Such failures are generally the result of the loss of active lead dioxide paste shedding from the current collector grid as a consequence of spalling and dimensional change deterioration that the active material undergoes during charging and discharging cycles.
U.S. Pat. No. 5,264,306 describes a lead acid battery system having a plurality of positive grids and a plurality of negative grids with respect of chemical pastes placed therein, where each of the grids has a mean plane and a matrix of raised and lowered portions formed in vertically oriented rows which alternate with undisturbed portions that provide unobstructed current channels extending from the lower areas of the grid plate to the upper areas of the grid plate with a conductive tab affixed thereto. However, the raised and lowered portions are oriented in the vertical direction as established by horizontally disposed slots. Further, the teachings of the grid specifically relate to lead-acid batteries. The teachings fail to consider the adverse impact of evolving boundary conditions resulting from the horizontally directed interruptions in the plate.
U.S. Design Pat. Des. 332,082 shows a battery plate grid of the sort which is described and used in lead-acid batteries as taught in U.S. Pat. No. 5,264,306. Both U.S. Pat. No. 5,264,306 and U.S. Design Pat. Des. 332,082 are incorporated herein by reference in their entireties.
The inventors have discovered that reorientation of raised and lowered portions of a current collector grid to a horizontal configuration (and correspondingly reorienting the grid channels) reduces or minimizes boundary conditions in the direction of current flow from lower portions to upper portions of the grid plate and to an associated collector tab structure for at least one of a positive electrode or a negative electrode.